Project Summary/Abstract The overall goal of the proposed project is to improve outcomes among individuals with knee osteoarthritis (OA) using a novel exercise method that can be included in rehabilitation approaches for disease management: high intensity interval training (HIIT). Unlike other physical activity interventions for knee OA currently available or under investigation, HIIT requires minimal time (10 minutes of exercise per session, 2 times per week) with the potential to quickly provide improvements in physical function, pain, and other health aspects. The rationale for the proposed research is built upon the proof that HIIT is effective in several clinical populations; however, the feasibility is unknown among individuals with OA, who face unique and substantial challenges to exercise, particularly functional limitations and pain. The main hypotheses of this line of research is that patients with knee OA will adhere to HIIT, report good tolerability of the program, and will have clinically important improvements in performance-based physical function, as well as knee strength, body composition, and cardiorespiratory fitness, after completing HIIT. A single-arm feasibility and proof-of-concept study of a 12- week HIIT intervention will be conducted in 30 patients with symptomatic knee OA. This study is innovative because it explores a novel rehabilitation approach, with potential for widespread generalizability, to improve physical function and pain in people with knee OA. In Aim 1, the multidisciplinary team, with expertise in OA, physical activity, cardiology, and biostatistics, will examine the feasibility and acceptability of a 12-week HIIT program in patients with symptomatic knee OA. We will determine adherence to and tolerability of HIIT, acceptability, and recruitment and retention rates of patients through 6- and 12-week assessments. In Aim 2, we will determine short-term changes at 6- and 12-weeks in outcomes of performance-based physical function, knee OA symptomatic burden (pain), balance, isometric knee extensor and flexor strength (factors associated with physical function and symptomatic knee OA progression), cardiorespiratory fitness, and body composition among patients with symptomatic knee OA participating in a HIIT intervention. If the HIIT intervention is shown to be well-tolerated and promising, results of this preliminary study will lay the foundation for a large randomized controlled trial to establish the efficacy of HIIT as a revolutionary approach for enhancing the rehabilitation and management of knee OA.